Idiom of the Day: canary in a coal mine

Something or someone who, due to sensitivity to his, her, or its surroundings, acts as an indicator and early warning of possible adverse conditions or danger. Refers to the former practice of taking caged canaries into coal mines. The birds would die if methane gas became present and thereby alert miners to the danger. Watch the video…: https://play.google.com/store/apps/details?id=com.tfd.mobile.TfdSearch